Production of iron for use in the manufacture of cast iron products



May 6, 1952 H. A. REECE PRODUCTION OF IRON FOR USE IN THE MANUFACTURE OFCAST IRON PRODUCTS 3 Sheets-Sheet 1 Filed May 16, 1950 RETAN ED STRE NGTH Y NE R WE 0 W w A A T R m H 5 m P SECTKDN May 6, 1952 H. A. REECEPRODUCTION OF IRON FOR USE IN THE MANUFACTURE OF CAST IRON PRODUCTS 5Sheets-Sheet 2 Filed May 16, 1950 iueaamem's Pam/man Low CARBON AQT TYCQEFHUENT E TKANSFORMATWN H\GH FERCENTAGE DEQDMPO5\T\ON PRDEUCT P WER IMELT \Gi SOU D\T PENETRAT NG WE K BASE META METAL Abs HARD ENEEs ADDGMPHT \ZERS $\L\C\DES OF ADD \ANZ'DENERS TELLU R\ UM TELLUR\U M SW W TIDa m 0 M M m w W 6N LE m- W M I cmuuwue.

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Patented May 6, 1952 PRODUCTION OF IRON FOR USE IN THE MANUFACTURE OFCAST IRON PRODUCTS Herbert A. Reece, Cleveland Heights, Ohio ApplicationMay 16, 1950, Serial No. 162,292

4 Claims. (CI. '7543) This invention relates, as indicated, to theproduction of iron for the use in the manufacture of cast iron products.

The iron-carbon system, stable and metastable, as proposed by Portevin,and shown on page 140 of The Elements of Ferrous Metallurgy, by

Rosenholtz and Oesterle, second edition, is of interest in showing thateutectic cast iron contains about 4.3% carbon, that the eutectic movesto the left, or lower carbon content, with silicon additions to the.metal, and as illustrating the percentage of cementite (FesC) possiblein relation to the eutectic.

The mathematical procedure of calculating the constituent percentages isillustrated in many books, both from the straight iron-carbon diagram,and with the introduction of various amounts of silicon where specificproperties or characteristics are desired in the metalp It is generallyagreed that the austenitic magma content of ordinary cast iron,containing from 1.25% silicon to 2.25%, is relatively in the maximum of40%-50%, where the total carbon content is 2.50% to 3%; 30%40%, wherethe total carbon content is3.00% to 3.15%; 20%-30%, where the totalcarbon content is 3.15% to 3.35%; and less than 20%, where the totalcarbon content is greater than 3.35%.

The tensile strength of products cast from- The theory of carbon-siliconratios, saturation value methods, the Maurer rectangle and other methodsfor the control of the physical properties of iron through methodsinvolving control of the chemical analysis, have all been exploited,with results which in general are unsatisfactory- The recent developmentof so-called nodular irons is a striking example of this, for withcarbonsilicon ratios based on the existing standards for obtaininglowest strength castings, these same ratios, through rearrangement ofthe constituents of'the casting, have produced strengths heretoforeunknown in iron castings.

I have discovered that by utilizing various carbon activity coefficientsin molten iron, and controlling the amounts of such carbon which areintroduced into the melt or cupola charge, I am able to control theproportions of austenite and cementite at the solidus, and therebycontrol the physical properties of the iron, including its strength,fluidity, machinability, damping capacity, etc.

By increasing the amounts of austenite at the solidus, the strength andsolidity penetrating power of the metal are improved, whereas byincreasing the amounts of the decomposition product, cementite, at thesolidus, the machinability and damping capacity of the metal areimproved. As the one constituent increases, the other decreases, foronly the two make up the metallic whole.

Through this method of control, I am enabled to obtain two groups ofcastings, as follows:

1. Castings derived from a predominating decomposition product at thesolidus (FesC or cementite).

2. Castings derived from a predominate transformation product at thesolidus (F6240 or austenite) By introducing carbon of various activitycoefficients in the molten iron in appreciable amounts, thesusceptibility of the molten iron to the formation of austenite at thesolidus is increased, resulting in an iron, which, when subjected tofurther graphitization treatments utilizing, for example, molybdenumsilicide, calcium silicide, ferrosilicon, or the like, has improvedstrength and toughness. In this manner, I have been able to producecast'irons having tensile strengths of up to 80,000 p. s. i., Withoutthe graphite .being in nodular form.

Similarly, by decreasing the amounts of such carbon in the molten iron,the metal becomes a decomposition product at the solidus, and while thestrength and toughness thereof are decreased, the damping capacity,machinability and lack of distortion are improved.

. The term or expression carbon activity coefficient is difiicult todefine, and must be defined in terms of the efiect produced by thecomponents of the melt. On this basis, it is possible to divide thecomponents or raw materials used for the manufacture of iron castings,whether steel pig iron, or cast iron scrap, as to their carbon activitycoefficient. The following table includes virtually every raw material,i. e., steel, pig iron and cast iron scrap, used in the manufacture ofiron castings in major amounts, and lists the approximate carbonactivity coeificient of each.

Carbon Activ- Raw Material ity Coefficient By using a mixture ofmaterials selected from the foregoing list, I can obtain a metal at thesolidus, which contains austenite in amounts necessary to obtain thedesired physical properties, and by controlling the silicon ionconcentration, I can retard or accelerate the precipitation of graphitein amounts necessary to produce a casting of the required physicalproperties.

In order to obtain a product of high physical properties, i. e., havingstrength and toughness, I start with a charge of selected carbonactivity value and with a sufficiently low silicon ion developmentpotential to prevent breakdown of the carbon before addition of agraphitizer, which may include ferro silicon, molybdenum silicide,calcium silicide, nickel, copper, etc., and thereby produce graymachinable iron castings.

In order to produce hard irons of greater strength and toughness thanwould ordinarily be obtainable without the use of the present invention,I add hardeners, such as chromium, tellurium, molybdenum, etc. Rapidcooling results in a decrease of the silicon ion mobility, and thecarbon ions produced do not tend to form graphite nodules. Thus,sufliciently fast cooling, as on chill work, may entirely preventgraphite formation.

In order to obtain the other class of castings, i. e., those which aredistortionless, and have low strength, but good clamping capacity, Iintroduce into the melt components, selected from the above list, havinglow carbon activity values, and preserve in the casting undissolvedgraphite molecules which results in a decomposition product at thesolidus, due to the fact that I have not saturated the liquid with suchcarbon and have left the graphite to promote the rapid breakdown of FeaCduring cooling.

In the accompanying drawings, which form a part of this specification,

Fig. 1 is a photomicrograph, illustrative of the first class ofproducts, and showing an austenitesorbite structure derived from a meltin which materials having high carbon activity coeflicients have beenintroduced. The quenching rate used in making this material exceeded thecritical cooling velocity of the metal, and at the solidus. more than70% austenite was present (as compared with maximums of 40%.50%austenite obtained through the use of existing methods). The chemicalanalysis of this sample showed a to control the carbon activity value ofthe liquidi total carbon content of 3.15%, silicon 1.61%, manganese.95%, phosphorus 12%, and sulphur .09%.

Fig. 2 is a photomicrograph illustrative of the other class of products,and showing a pearlite structure, derived from a melt in which materialshaving low carbon activity coefilcients have been introduced. Thequenching rate, in this case, was unable to exceed the critical coolingvelocity of the metal, since the melt was predominantly a decompositionproduct, rather than a transformation product. The chemical analysis ofthis sample showed a total carbon content of 3.28%, silicon 1.90%,manganese 32%, phosphorus .14% and sulphur .08%.

For high strength castings, the carbon activity content of the liquidmetal should be high, resulting in enriched austenite at the solidus.

A typical charge for obtaining such a high strength casting, that is tosay, a charge at the upper end of the scale of carbon activitycoefllcients, conducive to high transformation product recovery, is asfollows:

780# coil springs 220i; gates, risers, return scrap, etc. '7 siliconbriquettes 2 manganese briquettes The above charge is melted, and inorder to obtain the desired or proper grayness of the casting, the melthas added thereto a graphitizing addition, such as molybdenum silicide,calcium silicide, ferro silicon, copper, nickel, etc.

High carbon activity coefficient liquid melts are readily attacked bythe silicon ion and rarely require more than ounces of graphitizer perton of the liquid metal, in order to effect the desired grayness.

The solidity penetrating power of the high carbon activity coefiicientmelt is greatest when the graphitizing treatment is light, and leastwhere the graphitizing treatment is heavy, as illustrated by the factthat 25 ounces of the graphitizer are sufficient for a 12 inch sectioncasting, whereas ounces are necessary for a inch section casting.

The solidity penetrating power of the metal increases with the increasein carbon activity coefiicient, the percentage of the mix ingredientsbeing otherwise the same. This is illustrated by Fig. 3 of theaccompanying drawing, wherein the abscissa represents the thickness of acasting in inches. and the ordinate the percentage of retained strengthin the casting in ratio to thestrength of the test specimen. The solidlinecurve is the result of many tests and published results, and thebroken line curve represents values obtained by the use of the processof the present invention.

Acommon supposition of cast iron metallurgy is that the carbon contentof the iron decreases, the strength of the resultant castings willincrease. This is analogous to another principle of cast ironmetallurgy, that as the steel content ofthe charge increases, thestrength of the resultant product increases.

This inventor has long disagreed with these premises and regards liquidiron as a solution containing carbon of various activity coefilcients,wherein the carbon activity value of the charge isthe controllingmeasure of the product,-that is to say, the control of the physicalproperties of the resultant casting is based on the ability For example,ina charge composed of 5.0% steel 15% pig iron 35 returns 11 FeSi bricks4 Mn bricks having a calculated analysis of Si Mn P s 1.73 1.18 .19 .089

the carbon activity value of the charge is 50% steel x .50 .250 15% pigx .10 .015 35% returns X .23 .081

Carbon activity value .346 (Carbon activity value) 34.6% Now, if wechange the activity value of the charge and even use a lower steelcontent, viz: 40% steel X .83 .332 15% pig X .10 .015 45% returns x .23.104

Carbon activity value .451 (Carbon activity value) 45.1%

with the same chemistry, the higher carbon activity value iron will havehigher physical properties, even though the steel content is less.

As the carbon activity value of the solution increases, a higher siliconion potential is required to efiect the same degree of graphitizationand resultant physical properties, viz:

Graphitization Value in Percentage Silicon Carbon Activity Value PerCent 30 .10 35 .15 4o .20 45 .25 50 .30

Where a tough, hard casting is desired, a hardening treatment withhardening alloys or elements (tellurium, chromium, molybdenum,manganese, etc.) should be employed, this treatment being relatively onthe order of less than 2%.

Similarly, it would require a lesser amount of a carbide forming elementto advantageously effect the structure and resultant physicalproperties, viz:

Carbon Activity Value gg g g Percent 6.. activity coefficient, highdecomposition product, is obtained. A typical charge for such ajproductis as follows: 1 1

vso# hot blast pig iron 220# gates, risers, return scrap, etc.,fromsimilar melts w The above charge is melted, and is then graph,-itized or hardened, depending upon the properties desired in thecasting.

As an example of a treatment for a specific problem of eliminatingwarpage in a casting, the treatment, after melting, consisted in theaddition of /2 per cent of 30-70 ferro silicon, which resulted in aplate thickness, 32" square, fully enclosed in a frame 1%" thick, whichwas less than out of true.

Various combinations of the use of carbon activity coefiicient metal andits treatment are illustrated in Fig. 4 of the drawings. Castings of anyspecific service application can be produced by relating the applicationto the service desired in the casting.

Fig. 5 of the drawings is a diagram illustrating the relationshipbetween the carbon activity coefficient and equivalent tensile strengthsin various sections, the tensile strength remainin uniform as the carbonactivity coefiicient increases with the section. This illustrates thesolidity penetrating power of increases in the carbon activitycoefiicient. As shown in Fig. 6, 33% carbon activity value has a tensilestrength of 40,000 p. s. i. Thus; to obtain 40,000 p. s. i. tensilestrength in the 2" section, the carbon activity value must be 44%, andin the 6" section for 40,000 p. s. i. tensile strength, the activitymust be 82%.

Fig. 6 of the drawings is a diagram illustrating the relationshipbetween carbon activity and the tensile strength of A. S. T. M. B bar,the tensile strength increasing uniformly as the carbon activityincreases.

Fig. '7 of the drawings is a diagram illustrating the condition of theproduct at the solidus, as the carbon activity coefiicient factorincreases. The metal at the solidus passes from a decomposition product,to an austenitic magma product, to a transformation product.

Fig. 8 of the drawings is a diagram illustrating the relationshipbetween the raw material classification and the carbon activitycoefiicients.

It will be understood that various changes may be made in the steps ofthe method as described, and in other details of the process, withoutdeparting from the scope of the appended claims.

Having thus described my invention, I claim:

1. The method of producing cast iron of controlled physical propertiesincluding desired tensile strength, which comprises charging into amelting furnace a mixture of ferrous materials having a total carbonactivity coeflicient in percent substantially as indicated in Figure 6of the drawings with the total carbon activity coeiiicient of the chargeplotted against tensile strength on said Figure 6, the carbon activitycoefiicient in percent being substantially as indicated for variousferrous materials in Figure 8 of the drawings.

2. The method as set forth in claim 1 modified for castings of difierentcross sections wherein the carbon activity coefiicients in percent areplotted against equivalent tensile strength in sections of difierentsizes substantially as indicated in Fig. 5 of the drawings.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATESIPATENTS Number Name Date Reece Apr. 19, 1949

1. THE METHOD OF PRODUCING CAST IRON AND CONTROLLED PHYSICAL PROPERTIESINCLUDING DESIRED TENSILE STRENGTH, WHICH COMPRISES CHARGING INTO AMELTING FURNACE A MIXTURE OF FERROUS MATERIALS HAVING A TOTAL CARBONACTIVITY COEFFICIENT IN PERCENT SUBSTANTIALLY AS INDICATED IN FIGURE 6OF THE DRAWINGS WITH THE TOTAL CARBON ACTIVITY COEFFICIENT OF THE CHARGEPLOTTED AGAINST TENSILE